The invention relates to a cigarette manufacturing machine of the double rod type.
In a machine of this type, as disclosed for example in U.S. Pat. No. 4,336,812, two continuous bands or fillets of tobacco are formed by causing single particles of tobacco to collect beneath two respective supports. The supports are provided by the bottom branches of two conveyor belts disposed mutually parallel and looped around corresponding beams or supporting structures providing internal chambers connected to respective sources of suction. The conveyor belts are made of a material which is permeable to air, and the bottom of each chamber communicates with holes emerging onto the back of the respective belt, such that suction can be generated through the bottom branch of each belt and the corresponding fillet of tobacco thus supported from above as it forms. The fillets of tobacco are subjected to a skimming operation during their progress along the bottom branches of the belts, for ensuring a substantially constant thickness.
The tobacco is released from the ends of the belts at a respective transfer station, or position, and taken up by a further section of the machine in which formation of the two continuous cigarette rods is brought about.
This further section of the machine comprises a bed, of which the surface uppermost provides two channels disposed substantially parallel and in vertical alignment, at least initially, with the conveyor belts carrying the fillets of tobacco. The surface in question provides support to a pair of second conveyor belts fashioned from a deformable material likewise permeable to air, for example a fabric, which are capable of movement longitudinally along the two channels.
The bed also includes an inner chamber connected to a source of suction, and with holes departing from the chamber and terminating in the channels. Thus, a force of suction can be generated through the second belts sufficient both to anchor two strips of cigarette paper directed continuously into the channels, and, to attract and hold the tobacco released from the first conveyor belts. The use of suction, initially to support the fillet of tobacco, and thereafter to cradle the cigarette paper and the tobacco together, has been proven successfully useful as a feed system.
On the other hand, it has been discovered that this same suction generates a certain degree of negative pressure in the void existing between the first and second pairs of conveyor belts, or rather between the two structures providing support to the belts, which tends somewhat to destabilize the passage of the fillets of tobacco from the first belts to the second, and thus clearly to detract from a correct formation of the continuous cigarette rods.